Examples of projection objectives for microlithography are disclosed in U.S. Pat. No. 6, 266,389 B1, in US 2005/0134980 A1, in US 2007/0195317 A1, in US 2007/0058269 A1, in US 2007/0223112 A, U.S. Pat. Nos. 6,396,067 B1, in 6,361,176 B1 and in U.S. Pat. No. 6, 666,560 B2.